Devices for measuring the inclination of objects are known in the art. The most common inclination-measuring device is a level vial having a liquid and an air bubble enclosed in a tube. The tube is configured so that the bubble floats to the center of the tube when the level vial is placed on a level surface and floats to the sides of the tube when the vial is placed on an inclined surface.
A major deficiency of this type of device is that it only provides a visual indication of the inclination of the object. Another shortcoming of this device is that it does not provide an output signal suitable for input to other devices such as a controller.
Various devices have been developed in an attempt to solve this problem. For example, electrolytic levels are used as inclination measuring devices by partially submerging electrodes in an electrolyte liquid. As the electrolytic level is tilted, the amount of contact between the electrodes and the electrolyte liquid increases or decreases, thus changing the conductivity of the electrodes. This change in conductivity is converted to a signal representative of the inclination of the object. Unfortunately, this device is sensitive to temperature changes due to the expansion and contraction of the electrolyte liquid. Additionally, the sensitivity of the device can change over time if electrolysis or evaporation reduces the amount of electrolyte in the vial.
Inclination is also measured by using a low-g Micro Electro-Mechanical System (MEMS) accelerometer. Two types of MEMS are currently used. One is based on thermal sensing technology and the other is based on capacitive sensing technology. Both of these technologies are extremely sensitive to variations in ambient temperature. Extreme measures must be taken to calibrate and compensate these sensors for use in an automotive environment. Sensor data collected during the calibration process from the MEMS is used with a temperature-compensating algorithm in conjunction with an Electronic Control Unit (ECU) micro-controller. The micro-controller performs complex calculations and/or table look-ups to convert the acceleration signal into the corresponding inclination. This can be very time consuming when using small micro-controllers because of the lack of floating point math capabilities.
A number of contact sensors have also been proposed for use with inclinometers. One such contact sensor is a potentiometer slider with electrical means. With time, the slider surface wears or corrodes affecting its reliability and thus, contact sensors have not been used extensively in automotive applications.
Pendulum-activated devices have also been proposed to solve this problem. In general, they are simple and easy to fabricate. For example, U.S. Pat. No. 4,426,788 teaches the movement of a pivotally mounted pendulum to display a visual inclination indication. This device does not provide an electrical signal representative of inclination angle. Other pendulum-activated devices are disclosed in U.S. Pat. Nos. 4,887,359; 5,285,031; and 5,821,419. Each of these devices uses an electrically conductive pendulum to control the electrical current through an open and close switch assembly for connection with associated circuitry of a motor vehicle. However, these devices do not provide an electrical signal that varies with the inclination of the motor vehicle and each uses electrical contacts that can become corroded which does affect its reliability.
Thus, there is a need for a pendulum-activated device that uses a non-contacting rotary sensor and provides an electrical signal that varies with inclination, which is reliable, temperature insensitive, inexpensive, and easy to fabricate.
The present invention provides an inclination measuring device for a motor vehicle that includes a pendulum attached to the vehicle and a rotary sensor adjacent the pendulum and operatively connected thereto which is contact-less and produces a signal in response to the inclination of the vehicle.
From the foregoing and the following more detailed description of various preferred embodiments it will be apparent to those skilled in the art that the present invention provides a significant advance in the technology of inclination measuring devices. Particularly significant in this regard is the potential the invention affords for providing a high quality, easy to package, temperature insensitive, reliable, light weight, compact, and low cost inclination measuring device for use in a motor vehicle. Additional features and advantages of various preferred embodiments will be better understood in view of the detailed description provided below.
It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the inclination-measuring apparatus as disclosed herein, including, for example, specific dimensions, orientations, and shapes of the housing and pendulum will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity or illustration. All references to direction and position, unless otherwise indicated, refer to the orientation of the inclination-measuring apparatus illustrated in the drawings. In general, up or upward refers to an upward direction in the plane of the paper in FIGS. 1–5, 8, 11, 12A and 12B and down or downward refers to a downward direction in the plane of the paper in FIGS. 1–5, 8, 11, 12A and 12B.